[ODE] Distance constraint

[i-photon@comcast.net]

Ok, I spent some time sifting through the list and found that some guy already
asked a question like this (although it was "ball and socket with some radius"
instead of "distance constraint", which was what I was looking for). Anyhoo,
James Golding was right, it is as simple as a one DOF joint written as follows:

D = p1-p0;
r0 = R0*a0;
r1 = R1*a1;

m = 1/(sqrt(dot(D,D))-dist);  <- this done safely, of course

JL0 = D/m;
JA0 = Cross(D/m,r0);

JL1 = -D/m;
Ja1 = Cross(r1,D/m);

I tested it and it works flawlessly for one and two bodies at any velocity.
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